1. Field of the Invention
The invention relates to headgear for use with a mask suitable for the delivery of non-invasive positive pressure ventilation and for nasal CPAP treatment of sleep disordered breathing conditions such as obstructive sleep apnea.
2. Description of Related Art
Obstructive Sleep Apnea (OSA) is a disease characterised by excessive daytime sleepiness, loud snoring and daytime irritability. Other effects of OSA can include depression, high blood pressure, serious heart conditions, sexual problems, memory lapses, intellectual deterioration and morning headaches.
The treatment of OSA by the application of nasal Continuous Positive Airway Pressure (CPAP) was invented by Sullivan and is described in U.S. Pat. No. 4,944,310 (Sullivan, assigned to ResMed Limited). The technique involves the application of a flow of pressurised breathable gas (typically room air) to either the nose or nose and mouth of a patient while they sleep. The technique is said to “splint” open the airways. Typical treatment pressures are in the range of 3 to 20 cmH2O. Flows are up to approximately 200 L/min. The flow of pressurised air is produced by a blower and delivered to the patient via a patient interface. The blower and patient interface are joined by a conduit. Whilst there are other techniques for the treatment of OSA, such as surgery, the use of CPAP has become the “gold” standard.
For a particular patient, the pressure which is needed to maintain open airways can vary throughout the night and vary on different nights. U.S. Pat. No. 5,245,995 (Sullivan and Lynch, assigned to ResMed Limited) describes a method and device for varying the pressure in accordance with indications. For example, if the patient starts to snore, the pressure automatically increases, whilst in the absence of snoring, the pressure automatically decreases.
Non-Invasive Positive Pressure Ventilation (NIPPV) is another form of treatment for breathing disorders. In its most basic form, it involves a relatively higher pressure of gas being provided in the patient mask during the inspiratory phase of respiration and a relatively lower pressure or atmospheric pressure being provided in the patient mask during the expiratory phase of respiration. Typical treatment pressures are in the range of 3 to 30 cmH, 0.
In other NIPPV modes, the pressure can be made to vary in a complex manner throughout the respiratory cycle. For example, the pressure at the mask during inspiration or expiration can be varied through the period of treatment, as disclosed in international PCT patent application no. PCT/AU97/00631 (Berthon-Jones, assigned to ResMed Limited).
In this specification, any reference to CPAP is to be understood as embracing all of the above-described forms of ventilatory treatment or assistance.
One of the earliest patient interfaces for providing CPAP treatment was constructed to include a fibreglass model of the patient's nose. The model was adhered to the patient's nose each night and removed each morning. An advantage of this patient interface included the customised fit, which assisted in a good seal between the patient interface and the patient's airways. However, the use of adhesive to secure the mask was inconvenient and not desirable.
Another suitable patient interface is described in U.S. Pat. No. 5,243,971 (Sullivan and Bruderer, assigned to the University of Sydney), entitled “Nasal Mask for CPAP having Ballooning/Moulding Seal with Wearer's Nose and Facial Contours”. This patent describes a nasal mask with a soft face-contacting portion, and a rigid shell. The mask is held in position using headgear. The headgear is attached to the mask and passes around the back of the wearer's head. The patent depicts two sets of straps in the headgear. The first set comprised a pair of straps passing from the forehead region to the back of the head. The second set comprised a pair of straps passing from the nasal region of the mask to the back of the head.
Another known patient interface is the MIRAGE® nasal mask (by ResMed Ltd). This nasal mask includes a pair of headgear attachment points in the nasal region of the mask shell and a forehead support that includes another pair of headgear attachment points. The headgear includes a single piece of a soft, flexible composite fabric with a generally triangular back portion and four straps. The four straps include a pair of upper straps and a pair of lower straps connecting to the headgear attachment points on the forehead support and nasal mask shell respectively. At the end of each strap is secured a piece of hook material, which, in use, passes through a headgear attachment point and fastens on corresponding loop material on the strap. The generally triangular back portion engages the skull in the region of the occiput. The fabric stretches under a load. The base of the triangle is positioned near and generally in line with the upper straps. Each strap is approximately 2 cm wide and approximately 3 mm thick. The fabric is a composite of three layers. The inner layer, closest to the patient's head, is made from nylon. The middle layer is made from neoprene. The outer layer is made from loop material, suitable for engaging with hook fastening material such as Velcro™. The upper straps have an approximate length of 19 cm, from the end to the closest corner of the triangle, whilst the lower straps have an approximate length of 26 cm. Including the triangle, the upper and lower straps each have an approximate total length of 60.5 cm. The triangular back portion is an approximate isosceles triangle, with a base of approximately 13.5 cm and sides of approximately 9 cm.
Some patients open their mouths during sleep, which means that they may not receive the benefit of CPAP due to mouth leaks. Various solutions have been proposed for this problem. One solution is taught in U.S. Pat. No. 6,123,082 (Berthon-Jones, assigned to ResMed Limited), whereby the lips are held closed. Another solution is to use a mask that covers both the nose and mouth of the patient. An example of a mouth and nasal mask is described in U.S. Pat. No. 5,560,354 (Berthon-Jones, Calluaud, Lynch & Hely, assigned to ResMed Limited).
Another suitable mask system is the MIRAGE® full-face mask (by assignee ResMed Limited). The MIRAGE® full-face mask and headgear is illustrated in FIGS. 1, 2 and 3. Suitable headgear (102) for this mask (100) is constructed from a composite material of nylon, neoprene and loop material. The headgear similarly comprises a pair of upper (104) and a pair of lower straps (106) and a generally triangular back portion (108). The upper strap has a total length of approximately 610 mm as shown in FIG. 3. The straps have an approximate width of 25 mm, however, the upper strap has an approximate width of 19 mm. The triangular region has a base of approximately 15.5 cm and two equal sides of approximately 11 cm. The upper and lower straps are approximately 192 mm apart. In addition, the headgear includes a quick release mechanism (110), as described in the pending U.S. patent application Ser. No. 09/482,718 (Lithgow, assigned to ResMed Limited). The quick release mechanism provides a “rip-chord” that can be pulled upon to separate the headgear and remove the mask in an emergency. When the headgear is positioned on the patient's head, the quick-release mechanism is situated at the back of the head and the chord runs through loops towards the front of the mask system.
Patient interface arrangements include nasal masks, nose and mouth masks, nasal prongs and nasal pillows. In all forms of patient interface used with CPAP for treating sleep disordered breathing, there is a need to counterbalance the force of the pressurised air and to correctly position the interface. Since the patient must sleep with this interface, it is important that it be comfortable. From the manufacturing and distribution channel perspectives, it is advantageous if one size of headgear fits a large range of head shapes and sizes.
It should be noted that while there are many mask and headgear arrangements available for ventilators, respirators, aviator masks and other breathing apparatus, in general, these may not be suitable for use in the treatment of sleep disordered breathing because they are not sufficiently comfortable to allow the patient to sleep.
The present invention is directed towards providing headgear for holding and securing a mask for use in the treatment of sleep disordered breathing which improves patient comfort, is long lasting and fits a wide range of head shapes and sizes.